This invention relates to apparatus and manufacturing methods for pressure sensors that employ pressure-sensitive diaphragms. It relates in particular to apparatus and assembly methods, including mechanical and electrical features, for a discrete sensor sub-assembly having a solid-state sensing element that includes the sensing diaphragm. The sub-assembly provides a minimal configuration for testing the electrical response of the diaphragm to pressure variations, before assembly within a housing.
Typical solid-state pressure sensing elements mount a thin silicon diaphragm above an open chamber. Pressure variations cause the diaphragm to deflect into and out of the chamber. The deflections cause changes in an electrical parameter, typically capacitance or resistance, that can be measured and converted into pressure-responsive information.
The use of solid-state pressure sensing elements in hostile work environments typically requires a housing that surrounds and protects the sensing element from direct contact with the fluid being measured. One conventional housing has a metal base covered with a flexible isolation diaphragm that separates the sensing diaphragm from the fluid being measured, and that deflects with the changing pressure of the fluid. A non-corrosive, inert fill fluid is within the housing, between the isolation diaphragm and the sensing diaphragm, and transmits the pressure being measured to the sensing diaphragm. Electrical leads carrying signals from the sensing element to external contacts of the pressure sensor pass through an hermetic seal to exit from the housing. This seal is typically achieved separately for each contact with a glass-to-metal bond through the metal base.
The sensing element conventionally is tested after assembly within the housing. This results in needless expense of materials and labor, if the testing reveals a defect, for example, in the sensing element or the connections to it.
It accordingly is an object of this invention to provide an improved apparatus and manufacturing method for diaphragm pressure sensor devices, including a low cost testable format.
It is a further object of the invention to provide an improved method and apparatus for the low-cost manufacture of a silicon-diaphragm pressure sensor having superior performance.
Another object of the invention is to provide pressure sensor apparatus, and a manufacturing method for the apparatus, that employ a solid-state sensing element and that operates with minimal spurious signal artifacts due to mechanical disturbance, e.g., from distortion or other unwanted stress, of the sensing element.
Other objects of the invention will be apparent from the following description.